Total tannin content of foods of François' Langur in Fusui, Guangxi, China: Preliminary study

The most valuable plant organs are often particularly rich in essential elements, but also very well defended. The mechanisms through which herbivores obtain essential elements from these organs and avoid being hurt by defensive compounds have long been debated. In order to study the total tannin of the food plants and its potential influence on food selection of François' Langur (Trachypithecus francoisi), we studied the feeding behavior of a group of François' Langurs (n = 4) in Fusui Reserve between January and December 2006 via Focal Animal Sampling. We collected food samples confirmed to be used by langurs each month. We measured the total tannins (TT) of these samples using the Folin–Denis method. We compared the TT of the foods across plant parts and among plant species. The food mainly consisted of immature leaves, accounting for 58.5% of the annual diet. The remaining parts were mature leaves (12.1%), fruits (12.1%), seeds (10.6%), flowers (4.3%) and barks (2.4%). The food included trees, accounting for 44.0% of their annual diet, followed by shrubs 22.8%, lianas 19.6% and herbs 13.6%. The average TT found in food was 60.96 mg/g TAE ranging from 25.57 mg/g TAE (September) to 97.89 mg/g TAE (March). The monthly average TT did not vary significantly among months (p = 0.36). Despite the lack of information concerning the relationship between food selection and TT for this langur, the data, however indicate that they can tolerate food with high TT.